Motor-pump unit

ABSTRACT

The invention relates to a motor-pump unit for a motor vehicle brake system, comprising a motor and a pump which is provided with a shaft that is driven by said motor, with the shaft end being rotatably mounted by means of at least one bearing in an accommodating member having valves and connecting channels, said shaft driving displacement means which are disposed in a chamber that can be filled with pressure fluid. In order to improve vacuum filling of the brake system with pressure fluid, the invention discloses that the shaft end terminates into a free space, and that at least one connection is provided between the free space and the chamber.

TECHNICAL FIELD

The present invention relates to a motor-pump unit for a motor vehiclebrake system, comprising a motor and a pump which is provided with ashaft that is driven by said motor, with the shaft end being rotatablymounted by means of at least one bearing in an accommodating memberhaving valves and connecting channels, said shaft driving displacementmeans which are disposed at least in part in a chamber that can befilled with pressure fluid and in which the bearing runs at least inpart, and with the shaft end terminating into a free space.

BACKGROUND OF THE INVENTION

A motor-pump unit of this type is disclosed in DE 199 27 658 A1. Ingeneral, a motor vehicle brake system is filled with the necessarypressure fluid after the assembly of the individual system componentssuch as in particular a master brake cylinder, a tube and hose linesystem, the motor-pump unit and wheel brakes at the vehiclemanufacturer's premises. For this purpose, the entire brake system isevacuated in a first process step, while the pressure fluid provided isintroduced in a second process step.

It has shown that roller bearing assemblies of motor-pump units areexposed to high stress, which is untypical of roller bearings, inparticular during the pressure fluid filling process. Due to analternate application with vacuum or excess pressure, respectively, itmay e.g. occur in sealed roller bearings that sealing elements such assealing lips are detached. This fact, in turn, can cause lubricants tobe washed out and, consequently, can lead to a reduced lifetime of thepump. The bearings will fail prematurely what is problematic inparticular in brake systems with long pump operating times as is thecase in electrohydraulic brake systems in particular. Bearings, whichare not sealed, provide a free access to the roller surfaces and do notallow using a special lubricant. This entails problems when thelubricating properties of the pressure fluid used are not appropriate,or when the pressure fluid contains wear particles that can cause damageto the running surfaces.

BRIEF SUMMARY OF THE INVENTION

An object of the invention is to provide an improved motor-pump unitwhere the risk of bearing damages and the washout of lubricants frombearings is reduced.

According to the invention, this object is achieved because the bearingseparates the chamber from the free space, and because a connection isprovided between the chamber and the free space which acts quasi as abypass circumventing the interior of the roller bearing so that itneither must be feared that lubricants are washed out, nor that sealingmeans are damaged. The result is that sealed roller bearings can beused, which are protected against washouts of lubricants. A quick and,hence, low-cost pressure fluid filling process is rendered possiblenevertheless.

In a favorable embodiment of the invention, the free space and thechamber are destined to receive pressure fluid, in particular to receiveleakage pressure fluid, and there is further provision of a channelbetween a pressure fluid supply tank and the chamber so that the freespace can be connected to the pressure fluid supply tank especially forfilling purposes. With long pump operating times, it is thereforerendered possible to return the leakage pressure fluid, whichsuccessively accumulated in the chamber and the free space, into thepressure fluid supply tank and, thus, into the brake system.

In another favorable embodiment of the invention, the bearing isconfigured as a movable bearing in such a fashion that the connectionbetween free space and chamber takes place by way of a slot between aninner bearing ring and a seat of the roller bearing. This obviates theneed for making any special provisions to establish the connection.

In another embodiment of the invention, the connection is designed as achannel, with the channel's wall consisting of circumferential areas ofinner ring and the bearing seat. The channel may principally have anycross-section desired and allows the mentioned connection at a definedlocation.

When the bearing seat has at least one flattened region for forming thechannel, said flattened region is simple to produce by a metal-cuttingoperation during manufacture of the shaft. This fact avoids bypass boresat the housing end. The mounting space thereby saved in the housing canbe used for other purposes.

When the shaft includes an eccentric for driving at least one pumppiston, the maximum of the eccentricity and the channel are arrangedsubstantially in alignment with each other with regard to an axialdirection. The surface pressure on the inner bearing ring is reduced dueto this arrangement because the channel will not reduce the abutmentsurface available.

According to the invention, the bearing is arranged in a steppedthrough-hole of the accommodating member, with the bearing adjoining thefree space, and the through-hole and the free space being provided witha closure means. Manufacturing a through-hole is simple compared tomanufacturing a blind-end bore and, in addition, allows supporting theshaft end when mounting a bearing close to the motor.

The closure means is preferably designed as a cover that abuts on a borestep, with said cover being calked with the accommodating member. Thecover can be a deepdrawn or molded part, and the calking at the housingalso reduces the costs of manufacture. Principally, a tool-freeclinching engagement between the cover and the accommodating member ispossible without departing from the spirit of the invention. In thisrespect, provision must be made to ensure that the cover includes anappropriate profiling and is made of a harder material than theaccommodating member.

Another solution of the above-mentioned problem can be taken from analternative independent claim. The motor-pump unit comprises a drivingmotor shaft, which is mounted by means of at least one bearing so as tobe rotatable in the accommodating member. The bearing is interposedbetween an end plate of the motor and the crank chamber. The shaftdrives displacement means reaching up to the crank chamber. Theabove-mentioned problem is solved by providing at least one channellinking a side of the bearing remote from the crank chamber to a leakagedischarge channel for the crank chamber.

A favorable design of the embodiment disposes of a channel provided inthe accommodating member. The leakage volume that can be received isfurther increased because the channel opens into a chamber that isdelimited by the end plate and the accommodating member, said chamberbeing connected to the leakage discharge channel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional enlarged view of an embodiment of amotor-pump unit.

FIG. 2 shows a sketch for schematically illustrating the position of theeccentric and the channel.

FIG. 3 shows a solution where a side of a bearing that is remote fromthe crank chamber is in connection to a leakage discharge channel by wayof a channel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A motor-pump unit 1 for application in a motor vehicle brake system isconnected to wheel brakes (not shown), on the one hand, and to agenerator (not shown) such as a master brake cylinder with a pressurefluid supply tank, on the other hand. An accommodating member 2comprises at least six hydraulic connections for this purpose. The unitis especially appropriate and destined for electrohydraulic brakesystems being equipped with a high-pressure accumulator integrated at orin the accommodating member 2 and used to feed the wheel brakes. In thisarrangement, the master brake cylinder is only used for the brakingoperation in a case of emergency and primarily serves for the simulationof brake application forces.

The motor-pump unit 1 further comprises a pump 3 for feeding thehigh-pressure accumulator or for feeding wheel brakes and a motor 4 fordriving the pump 3. An electronic unit 14 for controlling and regulatingthe system is positioned on a side of the accommodating member 2opposite the motor 4, and electronic control and supply lines of themotor 4 extend through the accommodating member 3.

Motor 4 drives a pump shaft 5, which is rotatably mounted within astepped through-hole 6 by means of sealed bearings 7, 8. Bearing 7 isdesigned as a fixed bearing, while bearing 8 is designed as a movablebearing and, therefore, cannot accommodate axial forces. Pump shaft 5acts on displacement means for the pressure fluid. The illustratedpreferred embodiment relates to a radial piston pump wherein thedisplacement means are pump pistons 9, 10 terminating into a chamber 11that is arranged roughly centrically between the bearings 7, 8 and beingdriven by an eccentric connected to the shaft (not shown in thedrawings). The number of pump pistons is principally optional, withthree pistons being preferred because this minimizes pulsations andnoise development. A roller bearing 12, in particular a needle bearingis interposed between the eccentric and pump pistons 9, 10 for thepurpose of friction reduction. In order to return e.g. pressure fluidwhich has collected due to inside leakage in chamber 11 to the systemagain, (or when the chamber 11 is anyway flooded with pressure fluid), achannel 13 being connected to the pressure fluid supply tank opens intochamber 11. A shaft end 15 remote from the motor reaches up to a freespace 16 and penetrates a bottom 17 that is inserted into thethrough-hole 6 and abuts axially on an outer ring of bearing 8. A slotis disposed between shaft 5 and a through-hole through the bottom 18 forthe passage of pressure fluid. An inner ring of bearing 8 is arranged ina sliding fit on a shaft-end bearing seat 18, and a connection 19 isestablished between chamber 11 and free space 16. According to theembodiment, the connection is configured as channel 20, its wall beingcomposed of circumferential areas of inner ring and bearing seat. Toform the channel 20, the bearing seat 18 has a flattened region 21,while the inner ring is annular as before so that a sickle-shaped, freechannel cross-section prevails between these adjacent components for thepneumatic evacuation and the passage of pressure fluid. Eccentricity andchannel 20 are in axial alignment with each other for a bearing seat asgood as before, what can be taken from FIG. 2. More specifically, theflattened region 21 substantially adopts the same angular position asdoes the eccentric maximum (maximum stroke), as becomes apparent fromthe dash-dot line in FIG. 2. Because the maximum bearing forces in thedisplacement stroke are plotted on the side opposite to the eccentricmaximum (as viewed from the inner bearing ring), the effectiveforce-transmitting surface at the bearing seat is not reduced in spiteof channel 20. Damages to the bearing seat are thereby avoided.

The flattened region 21 can principally be replaced by the provision ofbores that extend through the interior of the shaft.

As can be taken from FIG. 1, the free space 16 includes a closure means22 configured as a cover and preventing the loss of pressure fluid onthe side of the electronic unit 14. The cover is placed on a bore step23 of the through-hole 6 and calked with the accommodating member 2 influid-tight and gas-tight manner. For the purpose of sealing the chamber11, a sealing element 25 is provided between eccentric and bearing 7 inthe area of the motor-sided shaft end 24, said sealing element beingarranged in a retaining member 26, whereby leakage fluid is preventedfrom propagating out of the accommodating member 2 in the direction ofmotor 4.

FIG. 3 exhibits an embodiment according to another solution in aso-called ‘cantilever’ bearing with a freely overhanging shaft end. A‘cantilever’ bearing of this type is widely known in motor-pump units ofvehicle brake systems. The prior-art constructions suffer from theshortcoming that alternate heating and cooling processes, in particularof the motor, are quasi able to cause an aspiration operation so thatleakage fluid disposed in the crank chamber can propagate due to adifference in pressure into the motor's interior. Damage to the fillingof the bearing with lubricants or a washout of lubricants as well asdamage to the sealing means of the bearing is possible.

Components and features in FIG. 3 that correspond to those in FIGS. 1and 2 have been assigned identical reference numerals. Repetition of therelated description is refrained from, while differences will bereferred to in detail in the following. A pump shaft 5 with an eccentricthat is arranged in the crank chamber 11 is used as a pump drive. Asealed bearing 7 is used for the mounting support of pump shaft 5, saidbearing being provided in front of an end plate 30 of motor 4 betweencrank chamber 11 and end plate 30. Said end plate 30 is made of aplastic material, closes the bowl-shaped motor housing and carries thesealed bearing 7 provisionally before the final assembly of motor 4 andaccommodating member 2 because an annular socket 31 encompasses part ofthe outer bearing ring.

The crank chamber 11 is connected to a leakage discharge channel 32which can discharge accumulated leakage fluid into a storage chamber 33of the unit 33, store it, or discharge it into the ambience. To be ableto reliably discharge the leakage fluid into storage chamber 33 withinthe electronic unit 14 without allowing a return flow of leakage fluidor ambient fluids in the direction of the crank chamber 11, theaccumulating member 2 can include a small tube 34 reaching into thestorage chamber 33, and an outlet of the small tube 34 is arranged at adistance from the free fluid level.

To prevent in addition that leakage fluid washes out lubricants and canpropagate through the sealed bearing 7 or, due to the undermining ofbearing seats, into a spacing 35 behind the bearing 7 and from thereinto the interior of the motor, the side of the bearing 7 remote fromthe crank chamber is connected to the leakage discharge channel 32 byway of one or more channels 13. To this end, the annular socket 31comprises one or more channels 13 that extend in the direction of thebearing seat in the end plate 30 remote from the crank chamber so thatcontact can be made with the spacing 35 disposed between a fire wall ofthe end plate 30 and the side of the bearing 7 remote from the crankchamber. Each channel 13 connects this side remote from the crankchamber with the leakage discharge channel 32 which discharges leakagesfluid that can collect in the crank chamber 11 and the spacing 35 eitherinto the ambience or into the storage chamber 33. The interior of themotor is protected against the ingress of leakage fluid in the area ofthe shaft's exit due to the described features. Even if leakage fluidpropagates through the bearing 7 is it possible to supply it to theanyway provided leakage cycle. The system and in particular the bearing7 is relieved from pressure under pneumatic aspects due to being linkedto the atmosphere. This will prevent leakage fluid or ambient fluid tobe pressed through the bearing 7 into the interior of the motor underthe effect of a pressure gradient. Besides, it is prevented that washersof the bearing 7 get detached under the effect of a pressure gradient.

Channel 13 may principally also be provided as a partial recess in theaccommodating member 2, as can be taken from FIG. 3. Further, channel 13may principally be provided at an outer bearing ring, what necessitates,however, a separate machining of the standardized component. Thechannels 13 are provided in the accommodating member 2 in a modifiedembodiment (not shown).

As can be seen in FIG. 3, it is not imperative that the channel 13 opensdirectly into the leakage discharge channel 32. The reason is that achamber can be interposed, which is delimited by the end plate 30 andthe accommodating member 2.

In general, the invention allows an extremely compact construction aswell as a highly improved protection of the motor 4 against leakagefluid, while remnants of water and/or leakage fluid (brake fluid) withinthe unit are avoided.

It goes without saying that the invention is applicable with manydifferent types of pumps, which suffer from a so-called inside leakage.The invention is principally also apt for the application in connectionwith a gear pump including e.g. pairs of internal geared wheels asdisplacement means.

LIST OF REFERENCE NUMERALS

-   1 motor-pump unit-   2 accommodating member-   3 pump-   4 motor-   5 pump shaft-   6 through-hole-   7 bearing-   8 bearing-   9 pump piston-   10 pump piston-   11 chamber-   12 roller bearing-   13 channel-   14 electronic unit-   15 shaft end-   16 free space-   17 bottom-   18 bearing seat-   19 connection-   20 channel-   21 flattened region-   22 closure means-   23 bore step-   24 shaft end-   25 sealing element-   26 retaining member-   30 end plate-   31 annular socket-   32 leakage discharge channel-   33 storage chamber-   34 small tube-   35 spacing

1. A motor-pump unit for a motor vehicle brake system, comprising amotor and a pump which is provided with a shaft that is driven by saidmotor, with the shaft end being rotatably mounted by means of at leastone bearing in an accommodating member, said shaft driving displacementmeans which are disposed at least in part in a chamber that is filledwith pressure fluid and the chamber surrounding at least a part of thebearing, and with the shaft end terminating into a free space within theaccommodating member, wherein the bearing separates the chamber from thefree space, and wherein a connection is provided between the chamber andthe free space, the connection being a channel with a wall whichconsists of circumferential areas of an inner bearing ring and a bearingseat of said shaft.
 2. Motor-pump unit as claimed in claim 1, whereinthe free space and the chamber are designed to receive pressure fluid,particularly leakage pressure fluid.
 3. Motor-pump unit as claimed inclaim 1, wherein the channel is provided between a pressure fluid supplytank and the chamber so that the free space is connected to the pressurefluid supply tank especially for pressure fluid filling purposes. 4.Motor-pump unit as claimed in claim 1, wherein the bearing seat of saidshaft has at least one flattened region that forms the channel. 5.Motor-pump unit as claimed in claim 1, wherein the shaft includes aneccentric for driving at least one pump piston, and wherein the maximumof the eccentricity and the connection are arranged substantially inalignment with each other with regard to an axial direction. 6.Motor-pump unit as claimed in claim 1, wherein the bearing is arrangedin a stepped through-hole of the accommodating member, wherein thebearing adjoins the free space, and wherein the through-hole is providedwith a closure means.
 7. Motor-pump unit as claimed in claim 6, whereinthe closure means is designed as a cover that abuts on a bore step, andin that the cover is calked with the accommodating member.
 8. Amotor-pump unit for a motor vehicle brake system, comprising a motor anda pump which is provided with a shaft that is driven by said motor, withthe shaft end being rotatably mounted by means of at least one bearingin an accommodating member, said shaft driving displacement meansreaching into a crank chamber, and said bearing is provided in front ofan end plate of the motor between the crank chamber and the end plate,wherein at least one channel is connecting a side of the bearing remotefrom the crank chamber with a leakage discharge channel for the crankchamber, wherein the channel opens into a chamber that is delimited bythe end plate and the accommodating member, and wherein the chamber isconnected to the leakage discharge channel.
 9. Motor-pump unit asclaimed in claim 8, wherein the channel is provided in the end plate.10. Motor-pump unit as claimed in claim 8, wherein the channel isprovided in the accommodating member.
 11. Motor-pump unit as claimed inclaim 8, wherein the channel is provided at an outer ring of thebearing.
 12. Motor-pump unit as claimed in claim 8, wherein the bearingincludes sealing washers.